1. Field of the Invention
The invention relates to a system for variably actuating valves by means of cams for internal combustion engines.
2. The Prior Art
Systems for variably actuating valves by means of cam disks are known from German Patent No. DE 38 33 540 A1. In such systems, a camshaft is supported in the cylinder head in a rotational manner and is supported in a fixed position relative to the valves to be actuated and their associated arrangements for transmitting the stroke. An arrangement for transmitting the stroke is guided in a fixed position and associated with each of the valves arranged in the cylinder head. The valves are closed via spring force. Such an arrangement for transmitting the stroke may be a swivelling or rocker lever arrangement, or a bucket tappet as shown in FIGS. 1 and 2 of this patent. In these known systems, an element for automatically compensating the play of the valve may be arranged between the driven element and the valve shaft. An element intended for adjusting the stroke of the valve is arranged and guided in the cylinder head. The position of this element can be varied. An intermediate element is supported on the above-mentioned, variable element. The position of this intermediate element can be varied and can be displaced on the variable element. Furthermore, this intermediate element engages a cam of the camshaft that is supported in the cylinder head in a fixed position, and also engages the arrangement for transmitting the stroke that is associated with the valve.
The intermediate element can be articulated on the pivot lever of the arrangement transmitting the stroke, or it may be guided in a straight line and driven by thrust, or it may be guided on the head of a bucket tappet in a circular track. (See FIGS. 1-3 of DE 38 33 540 A1). However, these systems have disadvantages in the way in which the intermediate element is guided or controlled via sliding surfaces, and the relatively non-compact design of the arrangements.
A device for adjusting the stroke of a gas-changing valve in the cylinder head of an internal combustion engine is known from German Patent No. DE 199 13 742 A1. In this device, a swivel lever is provided with a no-load cam on one end and a control track comprising a stroking cam, whereby these cams are engaged during the stroking movement by line contact with a transmission element driving a gas-changing valve. The swivel lever engages a cam in about the center via a roller that is acted upon by a resetting spring. During its pivoting movements effected by the cam and the resetting spring, this swivel lever is guided by means of a control lever that is rotationally supported coaxially in relation to the axis of rotation of a control shaft, on the one hand, and guided at its second end by line contact on a cam disk, on the other hand. This cam disk is mounted on a control shaft that extends in the cylinder head parallel with the camshaft and supported in a rotational or fixed manner. The control shaft determines by means of its position the starting position of the swivel lever and thus whether only the no-load cam, or to which extent the stroking cam of the control track on the swivel lever will become active during the stroke of the cam on the transmission element driving the gas-changing valve. This has disadvantages in that the swivel lever pivots about an approximately vertical axis in relation to the transmission element, and is guided by a stationary control lever. This requires a considerable amount of space above the valves in the cylinder head as well as mechanical expenditure.